Greencore, which makes own label sandwiches and chilled convenience food for the UK's biggest supermarket chains, said all other products from the factory have tested negative for equine DNA.

It has launched a "thorough and comprehensive" investigation into how Asda's Chosen By You 350g Beef Bolognese Sauce came to show 4.8% of equine DNA.

The Bristol factory, which employs around 200 staff and is one of 23 facilities that the company runs across the UK and United States, was the subject of a "full deep-clean shutdown" over the weekend.

The majority of Dublin-based Greencore's products are sandwiches and prepared meals. Its Bristol site specialises in chilled soups and sauces.

Asda took the bolognese sauce off the shelves last week and temporarily withdrew other Greencore products as a precautionary measure. However, Greencore said tests of its other products had all proved negative for horse DNA.

According to the food maker, the meat used in its products is supplied by regularly audited companies, which insist they, in turn, use approved suppliers.

The company said Asda was supportive of its plans to implement additional species screening procedures to avoid further contamination.

"In conjunction with independent experts, its customers and key suppliers, the company has launched a thorough and comprehensive investigation to fully determine how this incident could have occurred," it said in a statement on Monday.

Greencore's Beef Bolognese Sauce product represented £300,000m of the total group's £1.1bn turnover in its last financial year. It said products containing beef-related ingredients account for less than 10% of overall revenue.

With the Europewide scandal over the contamination of meat products, from beefburgers to lasagne, showing no sign of abating, study the issue in depth and learn all you need to know about how it came to this with our essential guide